It engages the oil pump and fills the oil galley to the other side of the engine...........broken oil drive on the end of the distributor or incorrect machine work on the galley part of the housing.
Thats the bad brand of distributor or is it the pro form.? one is good ,one is questionable at best,I get em mixed up.
But that was my thought....I might be way off base.
Is it only no pressure at idle and pressure at revs.... ..
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Yes the rings on the shaft.......machined improperly or not at all.......